Not to be confused with "Evil Twin" which is a completely different person who is an evil version of a character, the Dark Side is an internal evil persona of a character. It is often seen as a figure that must be defeated to gain control over one's own body and gain extra powers.

Used frequently in Anime to either recap past events or provide a back story for a character, either their origin story or their off-screen training of new attack. Sometime and entire episode/chapter would be a entire flashback.